private int ProcessExtraFieldWinZipAes(byte[] buffer, int j, Int16 dataSize, long posn)
{
if (this._CompressionMethod == 0x0063)
{
if ((this._BitField & 0x01) != 0x01)
throw new BadReadException(String.Format(" Inconsistent metadata at position 0x{0:X16}", posn));
this._sourceIsEncrypted = true;
//this._aesCrypto = new WinZipAesCrypto(this);
// see spec at http://www.winzip.com/aes_info.htm
if (dataSize != 7)
throw new BadReadException(String.Format(" Inconsistent size (0x{0:X4}) in WinZip AES field at position 0x{1:X16}", dataSize, posn));
this._WinZipAesMethod = BitConverter.ToInt16(buffer, j);
j += 2;
if (this._WinZipAesMethod != 0x01 && this._WinZipAesMethod != 0x02)
throw new BadReadException(String.Format(" Unexpected vendor version number (0x{0:X4}) for WinZip AES metadata at position 0x{1:X16}",
this._WinZipAesMethod, posn));
Int16 vendorId = BitConverter.ToInt16(buffer, j);
j += 2;
if (vendorId != 0x4541)
throw new BadReadException(String.Format(" Unexpected vendor ID (0x{0:X4}) for WinZip AES metadata at position 0x{1:X16}", vendorId, posn));
int keystrength = (buffer[j] == 1) ? 128 : (buffer[j] == 3) ? 256 : -1;
if (keystrength < 0)
throw new BadReadException(String.Format("Invalid key strength ({0})", keystrength));
_Encryption_FromZipFile = this._Encryption = (keystrength == 128)
? EncryptionAlgorithm.WinZipAes128
: EncryptionAlgorithm.WinZipAes256;
j++;
// set the actual compression method
this._CompressionMethod_FromZipFile =
this._CompressionMethod = BitConverter.ToInt16(buffer, j);
j += 2; // for the next segment of the extra field
}
return j;
}